Systems and Methods for Cross-Cell Carrier Aggregation for Coverage Balance Improvement

ABSTRACT

A system and methods that are performed by a macro cell and a user equipment (UE) to implement a carrier aggregation mode in a network. The system includes a macrocell including a first coverage area and a plurality of small cells, each of the small cells including a second coverage area wherein the plurality of second coverage areas substantially cover the first coverage area. The macro cell operates a first component carrier as a primary component carrier in a carrier aggregation enabled network and one of the small cells operates a second component carrier as a secondary component carrier in the carrier aggregation enabled network.

PRIORITY CLAIM/ INCORPORATION BY REFERENCE

This application claims priority to U.S. Provisional Application61/910,737 entitled “Systems and Methods for Cross-Cell CarrierAggregation for Coverage Balance Improvement,” filed on Dec. 2, 2013,the entirety of which is incorporated herein by reference.

BACKGROUND

Long-term evolution (“LTE”) is a wireless communication standard usedfor high-speed data for mobile devices and data terminals. LTE-Advancedis a major enhancement to the LTE standard. Within the LTE-Advancedstandard, carrier aggregation is used to increase the bandwidth, andthereby increase the bitrates. Carrier aggregation has been introducedin the 3rd Generation Partnership Project (“3 GPP”) Release 10(LTE-Advanced standard) to provide wider than 20 MHz transmissionbandwidth to a single device (e.g., user equipment or “UE”) whilemaintaining the backward compatibility with legacy UEs. Specifically,carrier aggregation may be defined as the aggregation of two or morecomponent carriers in order to support wider transmission bandwidths.Carrier aggregation configuration may be defined as a combination ofcarrier aggregation operating bands, each supporting a carrieraggregation bandwidth class by a UE. The bandwidth class may be definedby the aggregated transmission bandwidth configuration and maximumnumber of component carriers supported by a UE.

For intra-band contiguous carrier aggregation, a carrier configurationmay be a single operating band supporting a carrier aggregationbandwidth class. For each carrier aggregation configuration,requirements may be specified for all bandwidth combinations containedwithin a bandwidth combination set, as indicated by the radio accesscapabilities of the UE. Accordingly, a UE may indicate support ofseveral bandwidth combination sets for each band combination.

Under the current standards, each aggregated carrier is referred to asmultiple component carriers, wherein each component carrier can have abandwidth of 1.4, 3, 5, 10, 15 or 20 MHz and a maximum of five componentcarriers can be aggregated. The multiple component carriers are from asingle base station section and a single UE. As illustrated in FIG. 1,two exemplary component carriers may each have a bandwidth of 10 MHz tocombine for a total bandwidth of 20 MHz. In LTE-Advance carrieraggregations, two frequency carrier having different frequencies may bebundled together to enhance a peak throughput from a single UE. All ofthe control and signaling may be transmitted on a primary carrier, whilethe secondary carrier may be limited to handling the data channel. Withcarrier aggregation features enabled, the LTE-Advanced standard devicesupporting 20 MHz carrier aggregation may achieve downlink (“DL”)throughput of 100 Mbps.

SUMMARY

Described herein are systems and methods for cross-cell carrieraggregation for improved coverage balance. A an exemplary systemincludes a macrocell including a first coverage area and a plurality ofsmall cells, each of the small cells including a second coverage areawherein the plurality of second coverage areas substantially cover thefirst coverage area. The macrocell operates a first component carrier asa primary component carrier in a carrier aggregation enabled network andone of the small cells operates a second component carrier as asecondary component carrier in the carrier aggregation enabled network.

Further described herein is a method performed at a user equipment(“UE”) utilizing a plurality of component carriers including a primarycomponent carrier and a secondary component carrier. The method includesperforming signal quality measurements for a primary cell and aplurality of secondary cells, generating a measurement results reportincluding the signal quality measurements, transmitting the measurementresults report from the UE to the primary cell and operating in acarrier aggregation mode with a first component carrier served by theprimary cell as a primary component carrier and a second componentcarrier served by the one of the secondary cells as a secondarycomponent carrier.

Further described herein is a method performed by a base station of anetwork that is configured to operate in a carrier aggregation mode, thebase station operating as a primary cell. The method including receivinga measurement results report from a user equipment (UE), wherein themeasurement results report includes signal quality measurements for theprimary cell and a plurality of secondary cells, selecting an optimalconfiguration of a primary component carrier served by the primary celland a secondary component carrier served by one of the secondary cellsfor the UE based on the signal quality measurements and sending theoptimal configuration to the UE.

DESCRIPTION OF THE DRAWINGS

FIG. 1 (discussed above) shows an example of carrier aggregationincluding two component carriers each having a bandwidth of 10 MHz for atotal bandwidth of 20 MHz.

FIG. 2 shows an example of a network arrangement including two macrocells each having two component carriers with different coverage areasaccording to the embodiments described herein.

FIG. 3 shows an exemplary network configuration having cross-cellcarrier aggregation according to the embodiments described herein.

FIG. 4 shows an exemplary user equipment (UE) that is configured tooperate in carrier aggregation mode within the network arrangement ofFIG. 3.

FIG. 5 shows an exemplary method for implementing cross-cell carrieraggregation from a UE according to the embodiments described herein.

FIG. 6 shows an exemplary measurement object provided by the UEaccording to the embodiments described herein.

FIG. 7 shows an exemplary method for implementing cross-cell carrieraggregation from a base station according to the embodiments describedherein.

DETAILED DESCRIPTION

The exemplary embodiments may be further understood with reference tothe following description and the appended drawings, wherein likeelements are referred to with the same reference numerals. The exemplaryembodiments show systems and methods for cross-cell carrier aggregationfor improved coverage balance. More specifically, as opposed to usingcarrier aggregation through a single base station selection, theexemplary embodiments described herein may utilize cross-cell carrieraggregation. Cross-cell carrier aggregation may be defined as having aprimary carrier being from one base station (e.g., a macrocell) and asecondary carrier being from another base station (e.g., a femtocell).

When carrier aggregation is used, there may be a number of serving cellsfor each of the component carriers. The coverage of the serving cellsmay differ due to both component carrier frequencies and power planning,which is useful for heterogeneous network planning. A radio resourcecontrol (“RRC”) connection is handled by one cell, namely the primaryserving cell (“PCell”), served by the primary component carrier (“PCC”)for uplink (“UL”) and downlink (“DL”).

The other component carriers may be referred to as secondary componentcarriers (“SCC”) for uplink (UL) and downlink (DL), serving thesecondary serving cells (“SCells”). The SCCs are added and removed asrequired, while the PCC is changed at handover. Those skilled in the artwill understand that the PCell and SCells are logical constructsallowing for the addition of SCells as needed. The PCell is the maincell that is used for all RRC signaling and control procedures, whilethe SCell is considered an augmentation to the PCell.

As noted above, LTE-Advance carrier aggregation is currently defined asmultiple carriers from a single base station section and a single UE. Inmany cases, the frequencies of the primary carrier and the secondarycarrier may be very different. For instance, a typical frequency for aprimary carrier may be 700 MHz, while a typical frequency for asecondary carrier may be 5.8 GHz. This large difference in frequencyresults in a significant coverage difference between two bundledcarriers. Accordingly, this often leads to problems of coverageimbalance between the bundled carriers, and thereby diminishes any ofthe benefits of carrier aggregation. The exemplary embodiments aredescribed with reference to LTE carrier aggregation. However, it shouldbe noted that the exemplary embodiments may also be implemented withinany network that is capable of carrier aggregation.

FIG. 2 shows a configuration 200 of current LTE-Advance carrieraggregation including two macro cells 210 and 250, each having twocomponent carriers with different frequencies f1 and f2 and includingdifferent coverage areas. Specifically, each of the two macro cells 210and 250 includes a primary carrier and a secondary carrier. The f1frequency of macro cells 210 and 250 is shown as having a coverage area220, 260, respectively and represents the primary carrier. The f2frequency of macro cells 210 and 250 is shown as having a coverage area230, 270, respectively and represents the secondary carrier. Due to thelarge discrepancy between the f1 coverage area 220, 260 and the f2coverage area 230, 270, a UE accessing either of the macro cells 210,250 will have very limited use of carrier aggregation. For instance, theUE may only be able to utilize carrier aggregation while within thecoverage areas where the f1 coverage area 220, 260 overlaps the f2coverage area 230, 270 i.e., the coverage areas 230, 270 (f1+f2) of themacro cells. Once the UE travels outside of the overlapping coverageareas 230, 270 (f1+f2), the UE will lose the benefit of the secondarycell for carrier aggregation. Accordingly, the current LTE-Advancecarrier aggregation results in coverage imbalance among the macro cells.The macro cells 210 and 250 may be enhanced Node Bs (eNBs) of an LTEcarrier aggregation enabled network.

According to an exemplary embodiment described herein, cross-cellcarrier aggregation allows for the primary carrier base station to beseparated from the secondary carrier base station. Such separationbetween the base stations may permit a much more dense base stationdeployment for higher frequency carriers over the low frequencycarriers. Accordingly the resulting configuration may thus provideimproved coverage balance between the aggregated carriers.

The exemplary systems and methods described herein may be especiallyuseful within the conditions depicted in FIG. 2, wherein the primarycarrier is a low frequency LTE band (e.g., 700 MHz) under macro celldeployment and the secondary carriers are located in frequencies inmultiple GHz bands under femto cell deployment.

FIG. 3 shows a network configuration 300 of LTE-Advance carrieraggregation utilized with the exemplary systems and methods forcross-cell carrier aggregation. As opposed to the single macro cell basestation sector serving as the two component carriers, as depicted inFIG. 2, the network configuration 300 of FIG. 3 includes multiplesmaller femto cell base stations that are separate from the macro cellbase station. For instance, while the f1 coverage of the macro cells mayremain unchanged, each of the smaller femto cells may have a coverage off2 within the f1 coverage.

The network configuration 300 has two macro cells 310 and 350 having af1 coverage area 320 and 360, respectively. These f1 coverage areas 320and 360 are substantially the same as the f1 coverage areas 220 and 260described for the network configuration 300. However, in this example,each macro cell 310, 350 have corresponding femtocells 330, 335, 340 and370, 375 and 380, respectively. Each of these femtocells 330, 335, 340and 370, 375 and 380 has a corresponding f2 coverage area 332, 337, 342,372, 377, 382, respectively. Each of these f2 coverage areas 332, 337,342, 372, 377, 382 may cover substantially the same area as the f2coverage areas 230, 270 of the network configuration 200.

By including the plurality of femto cells 332, 337, 342, 372, 377, 382within the f1 coverage areas 320, 360 of the macro cells 310, 350,respectively, a great portion of the f1 coverage areas 320, 360 mayprovide the UE with the combined coverage frequency of f1+f2. In otherwords, the carrier aggregation coverage balance of the networkconfiguration 300 in FIG. 3 is greatly improved over the coveragebalance illustrated in FIG. 2. In addition, as shown in FIG. 3, thecoverage frequencies f1 and f2 remain the same. That is, the networkconfiguration does not require additional frequencies to be used toprovide the substantially overlapped coverage areas. It should be notedthat while the network configuration 300 depicted in FIG. 3 shows threefemto cells within each of the macro cells f1 coverage area, one skilledin the art will understand that any number of smaller separate femtocells may be deployed with the macro cells. It should also be noted thatwhile the smaller cells are described as femtocells, the smaller orsecondary cells may be any type of smaller cell, e.g., picocells.

FIG. 4 shows an exemplary user equipment (UE) 400 that is configured tooperate in carrier aggregation mode within the network arrangement 300.The UE 400 may represent any electronic device that is configured toperform wireless functionalities, specifically carrier aggregationfunctionalities. For example, the UE 400 may be a portable device suchas a phone, a smartphone, a tablet, a phablet, a laptop, etc. In anotherexample, the UE 400 may be a stationary device such as a desktopterminal. The UE 400 may include a processor 405, a memory arrangement410, a display device 415, an input/output (I/O) device 420, atransceiver 425, and other components 430. The other components 430 mayinclude, for example, an audio input device, an audio output device, abattery, a data acquisition device, ports to electrically connect the UE200 to other electronic devices, etc.

The processor 405 may be configured to execute a plurality ofapplications of the station 400. For example, the applications mayinclude a web browser when connected to a communication network via thetransceiver 425. In a specific exemplary embodiment, the processor 405may execute a carrier aggregation application. The UE 400 is capable ofoperating in a carrier aggregation mode and a single carrier mode. Thecarrier aggregation application allows the UE 400 to operate within thenetwork arrangement 300.

The transceiver 425 may be a hardware component configured to transmitand/or receive data. That is, the transceiver 425 may enablecommunication with other electronic devices directly or indirectlythrough the network based upon the operating frequencies of the network.In carrier aggregation modes, the transceiver 425 allows the UE 400 tocommunicate with both the primary cell and the secondary cell.

It should be noted that the processor 405 performing the functionalitydescribed herein for the carrier aggregation application is onlyexemplary. For example, the transceiver 425 may also perform some or allof the functionality of the carrier aggregation application. In afurther example, a separate integrated circuit that may or may notinclude firmware may perform the functionality of the carrier selectionapplication.

FIG. 5 shows an exemplary method 500 for implementing cross-cell carrieraggregation by the UE 400 when connected to the network arrangement 300according to the embodiments described herein. Accordingly, the entiretyof the method 500 may be performed by the UE 400. The method 500 willalso be described with reference to the UE 400 being within the f1coverage area 320 of the macro cell 310 of the network arrangement 300.

In step 510, the UE 400 receives a list of potential secondary cellsfrom the macrocell 310. FIG. 6 shows an exemplary measurement object 600provided to the UE 400 that includes the list of the potential secondarycells. In this example, the list will include the femtocells 330, 335and 340, the potential SCells for the macro cell 310. It should be notedthat the macro cell 310 may have communications with the femtocells 330,335 and 340 and will know that these femotcells 330, 335 and 340 areavailable as SCells. The macrocell 310 may then provide this informationto the UE 400 to simplify the measurements to be made by the UE 400.This list of potential SCells may be provided to the UE 400, forexample, by the UE 400 receiving a measurement object 600 as shown inFIG. 6. The measurement object 600 may be an RRC object that is receivedfrom the macro cell 310. For example, the list of potential SCells maybe added to RRC IE ScellToAddMod-r10, which is an information element(IE) of the LTE standard. The list may include all the potential SCellsusing a coverage frequency of f2, as depicted in the networkconfiguration 300 of FIG. 3. Other information that may be included inthe list is the Cell-IDs of the potential SCells, the absoluteradio-frequency channel numbers (“ARFCNs”), etc.

In step 520, the UE 400 that is capable of utilizing a plurality ofcomponent carriers may perform signal quality measurements on both aprimary component carrier and the secondary component carriers.Specifically, the UE 400 may perform the signal quality measurements forthe primary component carrier. The UE 400 may further perform the signalquality measurements for each of the potential SCells. Examples ofsignal quality measurements may include Reference Signal Received Power(RSRP) and Reference Signal Received Quality (RSRQ). However, any typeof signal quality measurement may be used. As described above, the UE400 received the list of potential SCells from the primary cell,including the cell IDs and frequency list. Thus, the UE 400 is aware ofwhich potential SCells for which the signal quality measurements shouldbe made. To carry through with the example of the UE 400 being in the f1coverage area 320 of the macro cell 310, the signal quality measurementsfor the primary cell will result in the measurements for the macro cell310 operating on the frequency f1. Similarly, the signal qualitymeasurements for the secondary cells will result in the measurements forthe femtocells 330, 335, 340 operating on the f2 frequency.

In step 530 the UE 400 may report the measurement results on the primarycomponent carrier to the primary cell, e.g., the macro cell 310. Forinstance, the UE 400 may utilize a UL control channel (e.g., a PhysicalUplink Control Channel (PUCCH)) to report the measurement results. Thesemeasurement results may provide an indication to the primary basestation (e.g., macro cell 310) to select the most optimal resource usageon the primary and secondary carriers. For example, the f1 frequency ofthe macro cell 310 may be selected as the primary component carrier andthe f2 frequency of the femtocell 330 may be selected as the secondarycomponent carrier based on the measurement results.

In step 540, the UE 400 will receive the primary component carrier andsecondary component carrier from the primary base station (e.g., macrocell 310). As described above, the assignments are made by the macrocell 310 based on the signal quality measurements provided by the UE 400to the macro cell 310. In step 550, the UE 400 operates in the carrieraggregation mode using the assigned primary component carrier andsecondary component carrier.

In step 560, for the purpose of secondary cell handovers, the UE 400 isaware of the potential SCells using the coverage frequency of f2. Asdescribed above, the UE 400 receives the list of potential secondarycells and is therefore aware of the potential SCells to which the UE 400may be handed over. For example, the UE 400 will be aware of thefemotcells 335 and 340 to which the UE 400 may be handed over to as thesecondary component carrier. Thus, if the UE 400 is instructed toperform a handover to one of the other SCells and the handover fails,the UE 400 may attempt to connect to another SCell in its list ofpotential SCells.

FIG. 7 shows an exemplary method 700 for implementing cross-cell carrieraggregation from a base station according to the embodiments describedherein. The method 700 will be described with reference to the macrocell 310 of the network arrangement 300. The entirety of method 700 maybe performed by the primary base station (e.g., the macro cell 310).

In step 710, the primary carrier base station (e.g., macro cell 310) mayreceive the measurement report from the UE 400. An exemplary measurementreport and the type of information included in the information reportwere described above.

In step 720, the macro cell 310 may select an optimal resource blockconfiguration for the primary component carrier and the secondarycomponent carrier. This selection of the primary component carrier andthe secondary component carrier is based on the measurement reportreceived from the UE. Carrying through with the example started above,the macro cell 310 may select the f1 frequency of the macro cell 310 asthe primary component carrier and the f2 frequency of the femtocell 330as the secondary component carrier.

In step 730, the macro cell 310 may inform the secondary carrier basestation (e.g., the femtocell 330 in the example started above) toallocate the appropriate resource configuration for the data channeltransmission to the UE 400. According to one embodiment, the cross-basestation signaling (e.g., the signaling between the macro cell 310 andthe femtocell 330) may be achieved via a message through a defined X-2interface between the base stations. For instance, the interface may besimilar to a COMP signaling between LTE base stations.

In step 740, for secondary cell handovers, the macro cell 310 mayprepare each of the femtocells 330, 335, 340 for handovers based on themeasurement report received from the UE 400. For instance, if a handoverto a preferred femtocell as indicated by the RRC message fails, the UE400 may be directed to try another cell in its list of femtocells. Thelist of femtocells may be, for example, ordered based on the respectivesignal strengths as measured by the UE 400. This preparation process maysimplify the handover in the case of high mobility of the UE 400.

The exemplary embodiments are described with reference to theLTE-Advanced carrier aggregation scheme that has certaincharacteristics. For example, in frequency-division duplexing (“FDD”),the characteristics include that the number of aggregated carriers maybe different in DL and UL, typically, the number of UL componentcarriers is equal to or lower than the number of DL component carriers.In addition, the individual component carriers may also be of differentbandwidths. Alternatively, when time division duplexing (“TDD”) is used,the number of component carriers and the bandwidth of each componentcarrier are the same for DL and UL. However, those skilled in the artwill understand that the exemplary embodiments may be applied to anycarrier aggregation scheme including those having differentcharacteristics from the LTE-Advanced scheme.

It will be apparent to those skilled in the art that variousmodifications may be made in the present invention, without departingfrom the spirit or scope of the invention. Thus, it is intended that thepresent invention cover the modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

What is claimed is:
 1. A system, comprising: a macrocell including afirst coverage area; and a plurality of small cells, each of the smallcells including a second coverage area wherein the plurality of secondcoverage areas substantially cover the first coverage area, wherein themacrocell operates a first component carrier as a primary componentcarrier in a carrier aggregation enabled network, and wherein one of thesmall cells operates a second component carrier as a secondary componentcarrier in the carrier aggregation enabled network.
 2. The system ofclaim 1, wherein the macrocell is an evolved Node B (eNB) of an LTEnetwork and the small cells are one of femtocells and picocells of anLTE network.
 3. The system of claim 1, wherein the macrocell receives ameasurement report from a user equipment (UE), wherein the measurementreport includes signal quality measurements for the macrocell and theplurality of small cells.
 4. The system of claim 4, wherein themacrocell assigns the primary component carrier and the secondarycomponent carrier based on the measurement report.
 5. A method,comprising: at a user equipment (“UE”) utilizing a plurality ofcomponent carriers including a primary component carrier and a secondarycomponent carrier: performing signal quality measurements for a primarycell and a plurality of secondary cells; generating a measurementresults report including the signal quality measurements; transmittingthe measurement results report from the UE to the primary cell; andoperating in a carrier aggregation mode with a first component carrierserved by the primary cell as a primary component carrier and a secondcomponent carrier served by the one of the secondary cells as asecondary component carrier.
 6. The method of claim 5, furthercomprising: receiving a list of the plurality of secondary cells,wherein the UE perms the signal quality measurements on the secondarycells based on the list.
 7. The method of claim 6, wherein the listincludes a cell ID and absolute radio-frequency channel numbers for eachof the secondary cells.
 8. The method of claim 5, further comprising:receiving an assignment of the primary component carrier and thesecondary component carrier from the primary cell.
 9. The method ofclaim 6, further comprising: performing a handover procedure to switchto a third component carrier served by a second one of the secondarycells as the secondary component carrier.
 10. The method of claim 9,further comprising: performing, when the handover procedure fails, afurther handover procedure to a fourth component carrier served by athird one of the secondary cells, wherein the third one of the secondarycells is selected for the further handover procedure based on the listof secondary cells.
 11. The method of claim 5, wherein the primary cellis an evolved Node B (eNB) of a Long Term Evolution (LTE) network. 12.The method of claim 5, wherein the secondary cells are one of femtocellsand picocells of an LTE network.
 13. A method, comprising: at a basestation of a network that is configured to operate in a carrieraggregation mode, the base station operating as a primary cell:receiving a measurement results report from a user equipment (UE),wherein the measurement results report includes signal qualitymeasurements for the primary cell and a plurality of secondary cells;selecting an optimal configuration of a primary component carrier servedby the primary cell and a secondary component carrier served by one ofthe secondary cells for the UE based on the signal quality measurements;and sending the optimal configuration to the UE.
 14. The method of claim13, further comprising: informing the one of the secondary to allocateappropriate resources for the UE to access the secondary componentcarrier.
 15. The method of claim 13, further comprising: preparing thesecondary cells for a handover.
 16. The method of claim 13, furthercomprising: generating a list of the secondary cells; and transmittingthe list to the UE.
 17. The method of claim 16, wherein the listincludes a cell ID and absolute radio-frequency channel numbers for eachof the secondary cells.
 18. The method of claim 13, wherein the primarycell is an evolved Node B (eNB) of a Long Term Evolution (LTE) network.19. The method of claim 13, wherein the secondary cells are one offemtocells and picocells of an LTE network.
 20. The method of claim 19,wherein the primary cell informs the one of the secondary cells via anX2 interface between the primary cell and the one of the secondarycells.